1. Field of the Invention
The invention relates to a process for regulating an artificial ventilating device and such device. The invention will be used in particular in the field of construction of medical equipment and in particular equipment to assist patients' inspiration.
2. Discussion of the Background and Pertinent Information
It is customary in the medical field to use a technique known as "Inspiration Assistance" or "Artificial Ventilation" in various cases, in particular when faced with neurological problems, respiratory failure and even during surgical operations and in post-operative phases. These techniques have been known for some considerable time, and endeavors are increasingly being made to reduce the barometric aggression for the patient when inspiration assistance is provided. Indeed, it should be noted that when a healthy individual has spontaneous natural ventilation, the individual causes inspiration by an internal negative pressure and expiration by compression of the volume of air in his or her airways or respiratory passages.
On the other hand, when under artificial ventilation, during the inspiration phase, a respirable gaseous fluid mixture is insufflated to the patient; the individual's airways are accordingly under positive pressure during the inspiration phase, and not under negative pressure as occurs naturally during spontaneous ventilation.
There is a known respiratory assistance device in which the artificial ventilation is controlled. In such device, the controlled ventilation acts as a prosthesis taking over the whole of the patient's ventilatory work. This is called total controlled ventilation.
Other ventilation techniques have been introduced which enable the patient to progressively take part in performing their respiratory function. One known assisted ventilation method utilizes auto-triggered ventilation and inspiration assistance. In this method, the negative pressure caused by this patient's inspiration triggers an inspiration phase either with a volume and duration fixed by the machine, or with the necessary gas flow rate to maintain a desired positive pressure which may be set by an operator.
Such known types of assisted ventilation have numerous disadvantages based primarily on the fact that the patient has to provide substantial inspiratory work, depending on the machine. Further, risks may be caused by such ventilation, such as risks of tachypnea, respiratory alkalosis, or hyperinsufflation.
More recently, other types of artificial ventilation such as closed loop type have been developed with the aim of avoiding an excessively abrupt change from totally controlled ventilation to exclusively natural spontaneous ventilation, to enable the patients to adapt gradually and increase his or her security. Among these are intermittent controlled ventilation, variable imposed ventilation, or the method of CO.sub.2 closed loop ventilation.
In an intermittent controlled ventilation device, there is imposed on the patient, for example, n control cycles to x spontaneous cycles. This type of ventilation has disadvantages residing in the difficulty of setting adjustment and the need for manual intervention to adjust the device as a function of the way in which resuscitation develops.
In a variable imposed ventilation method, the ventilation is controlled by a minimum ventilation per minute setting. In this device, a threshold number of liters of gaseous mixture insufflated per minute is set, and whenever the patient's ventilation falls below this threshold, the ventilator delivers the necessary number of controlled cycles to achieve this threshold. The main inconvenience or disadvantage of this type of imposed ventilation is reflected by the adverse risks that could be produced, such as tachypnea and/or hypercapnia due to a possible increase of CO.sub.2 level in arterial blood.
Analysis of the problems posed by inspiratory assistance for patients reveals the usefulness of limiting the aggressiveness of ventilation, and in an addition permanently directing artificial ventilation to take maximum account of the patient's spontaneous natural ventilation. This allows the patient to take over part of his or her respiratory work and thereby assist in rehabilitation and/or allows weaning or severance from the ventilatory assistance.
Known inspiratory assistance devices are disadvantageous in that manual intervention is frequently required by medical personnel as the devices are not regulated correctly to enable the inspiratory assistance to be adjusted in accordance with the efforts being made by the patient. Further, these types of devices are not without risk of hypo-ventilation or hyperventilation, as volume delivered during the insufflation phase is not entirely controlled.
An object of this invention is to provide an artificial ventilation device and a process for regulating an artificial ventilation device for patient inspiratory assistance which enable the various above-mentioned disadvantages of the known devices to be overcome.
One of the objects of this invention is to provide a process for regulating an artificial ventilation device which carriers out an intermediate mode of artificial ventilation between a current controlled ventilation mode and a natural spontaneous ventilation mode. This intermediate mode is carried out as a function of the patient's performance, and to takes into account the patient's own spontaneous ventilation.
This additional intermediate mode therefore makes it possible to conceive of a workable system capable of changing automatically between the two extreme modes of ventilation, i.e., from spontaneous ventilation to controlled ventilation, or vice-versa.
Another object of this invention is to provide a process for regulating an artificial ventilation device and a device for aiding the patient's inspiration in which the total tidal volume of respirable gaseous insufflated into the patient in each cycle is controlled.
Another object of this invention is to propose an artificial ventilation device for assisting the inspiration of a patient which, in particular, thanks to its regulating process, enables the insufflation characteristics to be improved by providing the patient with maximum inspiratory assistance when the effort required is maximum, i.e., at the start of inspiration.
Another object of this invention is to provide a regulating process for an artificial ventilation device and a device using it enabling the manual intervention on the part of the intensivist (i.e., the person attending and monitoring the artificial ventilation device and patient) to be minimized, relieving him or her of any requirements of readjustment in accordance with developments of resuscitation.
Other objects and advantages of the this invention will become evident during the course of the description that follows, which is given as a guideline only and which is not intended to limit the invention.
According to the invention, a regulating process is provided to regulate an artificial ventilation device to assist the volumetric inspiration of a patient. The artificial ventilation device allows a sequence of respiratory cycles as a function of the patient's requirements, such as frequency of respiration FR or respiratory rate RR. Each cycle can consist of an inspiration phase, during which the patient is administered a volume of respirable gaseous fluids referred to as the tidal volume VT, and an expiration phase. The patient exhibits his or her own natural spontaneous ventilation and an airway pressure PAW.
A theoretical satisfactory (i.e., optimum) value is set for the patient as a function of his or her condition and natural spontaneous ventilation. This theoretical satisfactory ventilation value is referred to as the optimum ventilation per minute Vmn. A minimum tidal volume value VT min to be inspired by the patient is also set. Further, the patient's maximum airway pressure PAWmax is set. The total tidal volume VT delivered to the patient in each respiratory cycle is controlled by the disclosed artificial ventilation device. The artificial ventilation is controlled as a function of the minute ventilation setting Vmn, the minimum tidal volume VT min, and the maximum airway pressure PAWmax to satisfy the equation Vmn=RR.times.VT, so that the artificial ventilation changes automatically from a spontaneous ventilation mode to a controlled ventilation mode, or vice versa, as a function of the person's spontaneous natural ventilation.
The artificial ventilation device of the present invention comprises a supply source or supply means for supplying respirable gaseous fluid. This supply source provides at least a pressurized amount of fluid supply at the time of artificial ventilation. In addition, means for piping the gaseous fluid to the patient are provided. The piping means comprise entering means for entering reference settings suitable for fixing an optimum theoretical ventilation per minute Vmn value for the patient, a minimum tidal value VTmin, and a maximum airway pressure value Paw max. The piping means further comprises a control means for controlling the total tidal value VT delivered to the patient in each respiratory cycle and a closed loop control means for controlling, in close loop fashion, the artificial ventilation of the device by, in each cycle checking the relationship Vmn=RR.times.VT, and acting on the artificial ventilation pressurized fluid supply in accordance with the patient's spontaneous natural inspiration, in order to cause the artificial ventilation to change automatically between spontaneous ventilation and controlled ventilation.
The present invention will be easier to understand upon reading of the following description accompanied by the appended drawings which form an integral part hereof.